The present invention relates generally to sorting apparatus and, more particularly, to apparatus for automatically grading and sorting articles, especially fruit, according to size, surface blemish and surface color.
The grading and sorting of fruit is a major cost factor for the fresh fruit industry. In the past, most grading and sorting has been performed by human labor, involving the visual inspection of each fruit and the manual depositing of such fruit into a number of separate receivers in accordance with a worker's assessment of the fruit's proper grade category.
In addition to being a slow process, manual grading and sorting of fruit has proven to be further deficient in that the workers' grading assessments are highly subjective, varying both with time and from worker to worker. Moreover, a single blemish or discolored area on one side of a fruit can occasionally escape detection during manual sorting.
Because of these deficiencies in the manual grading and sorting of fruit, there have been a number of attempts in the past to automate the grading and sorting process. Studies have been made, such as that described in U.S. Pat. No. 2,933,613 to J. B. Powers entitled "Method and Apparatus for Sorting Objects According to Color," which indicate that a measure of the surface color of fruit can be derived by computing a ratio of the intensity of reflected light having a first wavelength to the intensity of reflected light having a second wavelength. Accordingly, devices have been constructed and used for measuring the ratio of red light intensity to infrared light intensity received from the fruit surface. However, such devices have typically provided only a single measurement for each fruit, and have done so by inspecting only one side of the fruit. Since fruit can typically have contrasting colors for different portions of their surfaces, these devices have not been entirely successful.
Other studies have been made, such as that described in U.S. Pat. No. 3,867,041 to G. K. Brown et al entitled "Method for Detecting Bruises in Fruit," which indicate that bruised fruit reflect light to a markedly less degree than do unbruised fruit. Typical fruit grading devices that utilize this principle, however, make only a single measurement of the intensity of light reflected from the surface of the fruit. The devices do not detect abrupt variations in the reflectivity of the fruit surface, such as those commonly exhibited by surface blemishes in fruit, especially citrus fruit. Additionally, successful performance of such prior devices requires maintenance of a constant level of illumination, a requirement that is difficult to achieve in the environment in which such devices are typically used.
The sorting of fruit according to size has usually been performed in the past either by manual inspection or by a separate automatic sizing apparatus. This has necessitated multiple inspections of each fruit, thus aggravating the inefficiencies and performance drawbacks of such prior fruit sorting systems.
It will be appreciated from the foregoing that there is a definite need for a more reliable and more efficient technique for grading and sorting fruit according to size, blemish and color. In particular such a technique should utilize apparatus that performs merely one inspection of substantially the entire surface of each fruit, and should have sufficient resolution to detect even minute blemishes or flaws in the fruit surface and to allow grading into a relatively large number of categories. The present invention fulfills this need.